What is the evaluation and management of a short PR (P-R) interval?

Evaluation and Management of Short PR Interval

A short PR interval (<120 ms) in isolation without a delta wave or widened QRS in an asymptomatic patient requires no further evaluation and can be considered a normal variant, particularly in athletes; however, if accompanied by a delta wave and widened QRS (Wolff-Parkinson-White pattern), comprehensive risk stratification is mandatory due to sudden cardiac death risk. 1, 2

Definition and Recognition

• A short PR interval is defined as <120 ms on the surface ECG 1, 2
• The critical distinction is whether a delta wave (slurring of the initial QRS) and QRS widening >120 ms are present, which defines the WPW pattern versus isolated short PR 1, 2
• Short PR with delta wave occurs due to an accessory pathway bypassing the AV node, allowing early ventricular activation 2

Risk Stratification Based on ECG Findings

Isolated Short PR (No Delta Wave, Normal QRS)

In asymptomatic athletes or patients with isolated short PR interval without delta wave or QRS widening, no further cardiac evaluation is indicated. 1

• This represents either a normal variant or Lown-Ganong-Levine syndrome, neither requiring intervention in asymptomatic individuals 2
• Age-appropriate norms should be used when interpreting PR intervals, particularly adjusting for gestational age in infants 1

WPW Pattern (Short PR + Delta Wave + Wide QRS)

All patients with WPW pattern require comprehensive evaluation regardless of symptoms, as sudden cardiac death can be the first manifestation in approximately 50% of cases. 2

Mandatory Evaluation for WPW Pattern

Initial Assessment

• Detailed symptom history: palpitations, presyncope, syncope, or family history of sudden death 2
• 12-lead ECG: document PR interval, delta wave morphology, and QRS duration 1
• Echocardiography: evaluate for Ebstein's anomaly and structural cardiomyopathy, both associated with WPW 1, 2

Non-Invasive Risk Stratification

Exercise stress testing is the first-line non-invasive test to assess accessory pathway risk. 1, 2

• Low-risk features on exercise testing include:
  • Abrupt, complete loss of pre-excitation at higher heart rates 1
  • Intermittent pre-excitation during sinus rhythm on resting ECG 1, 2
• If these low-risk features are clearly demonstrated, competitive athletes may be cleared for participation 1

Invasive Risk Stratification

Electrophysiological study (EPS) should be performed when:

• Non-invasive testing cannot confirm a low-risk pathway or is inconclusive 1
• The patient is a competitive athlete involved in moderate or high-intensity sports (some experts recommend EPS for all such athletes regardless of non-invasive test results) 1
• Symptomatic tachycardia is present 2

High-risk criteria at EPS requiring ablation:

• Shortest pre-excited RR interval during induced atrial fibrillation ≤250 ms (≥240 beats/min) 1, 2
• Multiple accessory pathways 2
• History of symptomatic tachycardia 2

Management Decisions

Catheter Ablation Indications

Transcatheter ablation is recommended for:

• Shortest pre-excited RR interval ≤250 ms during atrial fibrillation at EPS 1, 2
• Symptomatic patients with documented tachycardia 1
• Competitive athletes with high-risk features who wish to continue sports participation 1

Conservative Management

Observation without ablation is appropriate for:

• Asymptomatic patients with clearly documented low-risk pathway features (intermittent pre-excitation or abrupt loss at high heart rates) 1, 2
• Patients who decline ablation after informed discussion of sudden death risk 2

Special Populations

Infantile Pompe Disease

• Short PR interval is present in 75% of infantile Pompe disease cases and appears on ECG alongside very tall QRS complexes 1
• When evaluating infants with cardiomegaly, short PR interval should prompt consideration of Pompe disease and measurement of serum creatine kinase 1
• Caution is needed with voltage calibration, as extremely high QRS voltage may lead operators to decrease gain, missing this diagnostic clue 1

Athletes

• Short PR interval without delta wave in athletes is a normal variant requiring no evaluation 1
• Athletes with WPW pattern require the same rigorous evaluation as non-athletes, with particular attention to sports participation decisions 1

Critical Pitfalls to Avoid

• Never dismiss WPW pattern as benign even in asymptomatic patients, as sudden death can occur without warning 2
• Do not confuse isolated short PR with WPW pattern—the presence or absence of delta wave and QRS widening completely changes management 1, 2
• Ensure proper ECG calibration when evaluating for short PR, particularly in conditions like Pompe disease where QRS voltage may be extremely high 1
• Use age-appropriate PR interval norms, especially in pediatric populations 1